Wave-transmission system



Nov. 6, 1928. 1,690,224

E. w. GENT WAVE TRANSMISSION SYSTEM Filed June 1, 1926 Patented Nov. 6,1928.

UNITED STATES 1,690,224 PATENT OFFICE.

EDGAR W. GENT, OF MORRISTOWN, NEW JERSEY. ASSIGNOR T WESTERN ELECTRICCOMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

WAVE-TRANSMISSION SYSTEM.

Application filed June 1, 1926. Serial No. 112,851.

This invention relates to wave transmission systems, and particularly tomeans for controlling the energy level of transmission in such systems.

An object of the invention is to adjust the energy level in a wavetransmission system in response to changes in the intensity of thetransmitted waves. Other objects of the invention are to stabilize theoperation and facilitate the maintenance of such systems.

In radio broadcasting and public address systems, where music and speechare transmitted to a distant point over telephone or other transmissioncircuits, it is desirable to maintain the transmitted Waves at aconstant energy level. This has usually been accomplished by connectinga volume indicator across the outgoing circuit to indicate changes inthe energy level of the transmitted waves. An operator observes thedeflection of the volume indicator and manually adjusts the gain of anamplifier in the outgoing circuit to maintain the desired energy level.

The present invention provides an automatic system of volume controlwhich requires practically no maintenance and also eliminates theelement of inaccuracy which usually exists in manually controlledsystems. According to the invention an impedance element, such as aselenium cell, responsive to radiant energy, is included in the inputcircuit of the transmitting amplifier. The resistance of the seleniumcell is controlled by means of a light valve which permits light ofvarying intensity to fall on the cell in response to changes in theenergy level of the transmitted waves. Changes in the energy level ofthe transmitted waves thus produce a compensating change in the gain ofthe amplifier which tends to maintain the outgoing waves at a fixedenergy level.

The invention will be described in connection with the accompanyingdrawing which is a diagrammatic illustration of a transmission systemembodying the invention.

In the drawing, a microphone l is coupled to a multi-stage amplifier bymeans of a transformer 2. The amplifier comprises a plurality ofthree-electrode space discharge tubes 3, i and 5 connected in tandem,and provided with the usual sources of electrical energy'to properlypolarize the grid electrodes, to heat the cathodes, and to furnishanode-cathode current, respectively. The output circuit of the spacedischarge tube 5 till is coupled by means of a transformer 6 to anoutgoing circuit 7 whence the amplified Waves are transmitted to adistant station.

The microphone 1 is also coupled by means of a transformer 8 to a branchcircuit which is utilized for controlling the energy level of thetransmitted waves. This circuit includes a rectifier 9 which may be ofthe type disclosed in Patent No. 1,523,827 to E. L. Nelson, issuedJanuary 20, 1925, having a substantially infinite input impedance sothat it will absorb a negligible amount of energy from the signalingcircuit. The grid of the rectifier is so polarized that the steadyoutput current increases in response to increases in the input current.

The output circuit of the rectifier 9 is connected to the-movable string10 of a light yalve 11 which may be of the type disclosed in a copendingapplication of H. E. Ives, Serial No. 711,755, filed May 8, 1924. Thedisplacement of the string 10 causes a variation in the quantity oflight from a source 12 falling on a selenium cell 13, in accordance withvariations in the current received from the signaling circuit. The lightvalve is so arranged that an increase in the current in the string 1-0causes an increase in the quantity of light falling on the seleniumcell. The resistance of the selenium cell decreases as the quantity oflight falling on the cell increases.

The selenium cell 13 is connected in series with a potentiometer la inthe grid circuit of the amplifier tube 4, and hence the proportion ofthe voltage across the potentiometer 14. decreases as the resistance ofthe selenium cell decreases. Variations in the voltage across thepotentiometer produce corresponding variations in the gain of theamplifier, the gain of the amplifier decreasing, for example, whentheresistance of the selenium cell decreases. It will thus be seen that anincrease in the current in theinput circuit of the rectifier 9 willproduce a compensating decrease in the gain of the amplifier in thesignaling circuit, while a decrease in the current in the inp-utcircuitof the rectifier will produce a compensating increase in the gain of theamplifier. As a result of this action the gain of the amplifier .willvary gradually and. continuously in accordance with variations in theamplitude of the current received from the signaling circuit.

The speed of operation of a selenium cell.

its

is dependent to a certain extent upon the physical dimensions of theselenium material and by adjusting the gain of the amplifier inaccordance with variations in the impedance of a selenium cell, thespeed of operation of the system is slow enough to prevent suddenchanges in the gain adjustment which might affect the uality of thetransmitted speech or music, and serves to adjust the gain of theamplifier by an amount which will maintain a satisfactory output level.

The invention is also capable of other modifications and adaptations notspecifically referred to but included within the scope of the appendedclaims.

What is claimed is:

1. A wave transmission system-comprising a source of electrical waves ofvarying amplitude, a transmission medium, a space discharge amplifyingdevice having an input circuit connected to said source and suppliedwith said electrical waves, and having an output circuit connected tosaid medium, an element in said input circuit the impedance of which toelectrical currents varies in accordance with the quantity of radiantenergy impressed thereon, and means for supplying to said elementradiant energy varying directly in accordance with the amplitude of saidelectrical waves, whereby the energy level of the electrical wavesimpressed on said medium by said amplifying device is controlled.

2. A wave transmission system comprising a source of electrical waves ofvarying amplitude, a transmission medium, a space discharge amplifyingdevice having an in ut circuit connected to said source and supp iedwith said electrical waves and an output cireuit connected to saidmedium, a selenium cell in said'input circuit, a source of light waves,and means automatically varying the quantity of light from said sourcefalling on said cell and thus the impedance thereof in accordance withthe varying amplitude of said electrical waves to adjust the gain ofsaid amplifying de ice in such manner as to maintain the energy level ofthe electrical waves supplied to said medium substantially constant.

3. In a wave transmission system, a source of electrical waves ofvarying amplitude, a transmission medium over which said waves are to betransmitted, and means for maintaining the energy level of the wavessupplied to said medium substantially constant comprisinga spacedischarge device having a cathode an anode and a control electrode,

and an input and an output circuit, said EDGAR W. GENT.

